Electrical and optical properties of light-emitting field-effect transistors based on MEH-PPV polymer composite films with ZnO nanoparticles

The optical and electrical properties of light-emitting field-effect transistor structures with an active layer based on nanocomposite films containing zinc oxide (ZnO) nanoparticles dispersed in the matrix of the soluble conjugated polymer MEH-PPV have been investigated. It has been found that the current-voltage characteristics of the field-effect transistor based on MEH-PPV: ZnO films with a composite component ratio of 2: 1 have an ambipolar character, and the mobilities of electrons and holes in these structures at a temperature of 300 K reach high values up to ～1.2 and ～1.4 cm²/V s, respectively, which are close to the mobilities in fieldeffect transistors based on ZnO films. It has been shown that the ambipolar field-effect transistor based on MEH-PPV: ZnO films emits light at both positive and negative gate bias voltages. The mechanisms of injection, charge carrier transport, and radiative recombination in the studied structures have been discussed.     

电压调制变色有机电致发光器件中的能量传递

研究了不同掺杂浓度下PVK：Rubrene的光致发光及电致发光的特性。发现掺杂浓度较低的PVK：Rubrene的光致发光与电致发光有较大差别,这是Foerster能量传递及电致发光中陷阱中的电子对空穴的吸引作用使得PVK激子在光致发光和电致发光中的复合速率不同造成的。同时各掺杂浓度在5wt%以下的PVK：Rrbrene发光随电压的增加呈现变色,这是能量传递不完全时,未参与能量传递的PVK激子复合速率随电压升高增大的结果。     

掺杂DCJTB聚合物电化学池（LEC）的发光性质

通过在聚合物电化学池(LEC)发光器件的发光材料MEH-PPV中掺杂红光染料DCJTB,对LEC器件的发光性质进行研究。基于器件结构为ITO/MEH-PPV PEO LiCF3SO3/Al的薄膜LEC器件,其电致发光峰在570nm左右,通过在MEH-PPV与PEO的混合膜中掺杂不同比例的红光染料DCJTB,随着掺杂比例的增加,器件的发光峰由570nm向红光波段移动,通过控制DCJTB的掺杂比例制备了发光峰在570~650nm连续变化的LEC电致发光器件。对其分析认为从LEC主体发光聚合物MEH-PPV到染料DCJTB间发生了良好的能量传递。     

掺杂PVK光电特性研究

将磷光材料三-（2-苯基吡啶）-铱[Ir（ppy）3]掺杂在聚乙烯基咔唑（PVK）中作为发光层,制作了多层有机电致发光器件。采用常规的光电测量方法,研究其光致发光及电致发光特性,得到了激子形成截面随电压的变换关系。     

Electroplex emission at PVK/Bphen interface for application in white organic light-emitting diodes

White organic light-emitting diode (WOLED) with a structure of ITO/poly(N-vinylcarbazole) (PVK)/4,7-diphenyl-1, 10-phenanthroline (Bphen)/tris(8-hydroxyquinoline)aluminum (Alq₃)/LiF/Al has been fabricated via the thermal evaporation technique. The electroluminescence (EL) spectrum of the as-fabricated WOLED covers from 380 to 700 nm of the visible light region with a wide blue emission from PVK and an interesting new red emission. The red emission at 613 nm in EL spectra of the WOLED was attributed to electroplex emission at PVK/Bphen interface since it was not observed in photoluminescence spectra. The WOLED showed a Commission International De l'Eclairage coordinate of (0.31, 0.32), which is very close to the standard white coordinate (0.33, 0.33).     

Ir(Fppy)_3掺杂PVK体系发光特性的研究

对蓝色磷光材料Ir(Fppy)3不同浓度掺杂PVK薄膜的光致发光(PL)和电致发光(EL)特性进行了研究。并制备了结构为ITO/PEDOT:PSS/PVK:Ir(Fppy)3/BCP/Alq3/LiF/Al的蓝色磷光有机电致发光器件。实验结果发现,磷光材料掺杂浓度不同,器件发光特性不同。当Ir(Fppy)3掺杂浓度比较低时,EL光谱中可以观察到PVK较弱的发光;当Ir(Fppy)3掺杂浓度较高时,会发生浓度猝灭;当Ir(Fppy)3掺杂浓度比较适中时,EL光谱中观察不到PVK的发光,只有Ir(Fppy)3的发光。通过I-V-L特性的比较,当掺杂浓度为4%时,器件的光电特性最好。     

电场诱导聚合物分子取向对单线态和三线态激子形成截面的影响

通过对聚乙烯咔唑(PVK) 掺杂三(2-苯基吡啶)铱(Ir(ppy)₃)和4-二氰亚甲基-2-叔丁基-6-(1,1,7,7-四甲基久咯呢定基-9-烯基)-4H-吡喃(DCJTB)，PVK 掺杂DCJTB和PVK掺杂Ir(ppy)₃聚合物在成膜时高压电场作用下分子取向变化对单线态和三线态激子形成截面的研究，发现，随着成膜时电场的增强，单线态激子的形成截面在增加，而三线态激子的形成截面却减小. 关键词： 分子取向 激子形成截面 三线态 单线态     

MBE-grown Si: Er light-emitting structures: Effect of implantation and annealing on the luminescence properties

Features appearing in the photo-and electroluminescence spectra of light-emitting structures based on MBE-grown Si: Er layers are studied. The luminescence properties of Si layers implanted by Er and O ions were used as a reference. The temperature quenching of the photoluminescence intensity of Er-containing centers in MBE-grown and implanted layers can be approximated adequately by the same functional relationships with equal activation energies but with preexponential factors differing by more than two orders of magnitude. It is shown that the electroluminescence of Er³⁺ ions can be increased by additional coimplantation of erbium and oxygen ions into MBE-grown light-emitting diode structures and subsequent annealing. After this treatment, the Er-containing centers continue to dominate the luminescence spectrum.     

Influence of dipole moments on light-emitting features of cardo-type 1H-pyrazolo[3,4-b]quinolines

Several 1H-pyrazolo[3,4-b]quinoline derivatives were synthesized from 9,9′-di(p-aminophenyl)fluorene as possible dye chromophore for the organic light-emitting diodes. All the compounds exhibit strong fluorescence in solution and in solid state as well. The maximally achieved brightness was 65 Cd/m² and spectral range of electroluminescence (EL) covers the wavelength ranges from 420 up to 470 nm. The prepared compounds were used as dye luminophores in poly(N-vinylcarbazole) (PVK) matrix for single-layer EL light-emitting device. Principal goal of the work consists in an establishment of a possibility to operate by their light-emitting features (spectral positions of emitting lines, efficiency of electroluminescence, brightness, etc.) by appropriate changes of state dipole moments of the particular chromophore determined by semi-empirical quantum chemical calculations. The principal physical mechanism of such effects is explained within dipole-dipole interactions between the dye chromophores and PVK polymer chains.     

Temperature and concentration dependences of the photoluminescence of MEH-PPV polymer composite films with ZnO nanoparticles

The absorption and photoluminescence (PL) spectra of MEH-PPV: ZnO composite films have been investigated at different concentrations of ZnO nanoparticles and at different temperatures (in the case of PL). It has been shown that, at 297 K, with increasing concentration of ZnO nanoparticles in the composite, the intensity of the PL lines of MEH-PPV decreases, whereas the intensity of the PL lines of ZnO increases. At a relatively low concentration of ZnO nanoparticles, a decrease in the temperature leads to an increase in the intensity of PL lines associated with MEH-PPV and ZnO, whereas at higher concentrations of ZnO nanoparticles, the intensity of these lines decreases. This is accompanied by a slight shift in the maximum of the PL toward the infrared (IR) region and a narrowing of the PL line of MEH-PPV with a decrease in the temperature and with an increase in the ZnO concentration. The mechanism of energy transfer in composite systems consisting of a polymer and inorganic nanoparticles that can be responsible for the observed effects has been discussed.     

Mechanisms of visible electroluminescence in diode structures on the basis of porous silicon: A review

The main mechanisms of the visible electroluminescence (EL) of porous silicon are reviewed. Characteristics of photoluminescence and EL of diode structures based on porous silicon are compared. Metals having a smaller value of the electron work function (3.6 eV, Mg) than do Al and Au are proposed as the material for making contacts in such diode structures to increase the efficiency of their EL in the visible region of the spectrum. The main problems and prospects of light-emitting devices based on porous silicon are formulated.     

High performance polymer light-emitting diodes doped with a novel phosphorescent iridium complex

High performance polymer light-emitting diodes (PLEDs) based on a phosphor of noble metal complex bis(1,2-dipheny1-1H-benzoimidazole) iridium (acetylacetonate) [(pbi)₂Ir(acac)] doped in poly(N-vinylcarbazole) (PVK) host with various concentration were demonstrated. The photoluminescence (PL) and electroluminescence (EL) spectra of the PLEDs exhibited an emission intensity decrease of PVK and a gradually enhanced feature of (pbi)₂Ir(acac) with increased doping concentration. The device with a 5 wt% (pbi)₂Ir(acac) doped PVK system showed a high power efficiency of 3.84 lm/W and a luminance of 26,006 cd/m². The results indicated that both energy transfer and charge trapping have a significant influence on the performance of PLEDs. The devices have a broadened EL spectrum of full-width at half-maximum (FWHM) more than 100 nm, which can be realized for WOLEDs.     

Improved electrical and optical properties of MEH-PPV light emitting diodes using Ba buffer layer and porphyrin

It has been found that insertion of a thin Ba buffer layer between the Al electrode and the MEH-PPV layer results in a significantly higher current density in ITO/MEH-PPV/Al polymer light-emitting diodes due to a reduction of the potential barrier at the cathode-polymer interface. The photoluminescence is found to increase with the addition of porphyrin-containing platinum as the central atom, showing that some of the triplet excitons decay radiatively as a result of mixing porphyrin.     

掺杂不同一维纳米材料的空穴缓冲层对有机电致发光器件性能的影响

对一维纳米材料在空穴缓冲层PEDOT中的作用进行了研究。光致发光表明在PEDOT中掺杂一维纳米材料(二氧化钛纳米管和氧化锌纳米棒)可以提高双层样品PEDOT/MEH-PPV的发光效率。拉曼光谱的结果说明正是由于一维纳米材料与PEDOT之间存在的强相互作用,才减少了PEDOT/MEH-PPV界面上猝灭发光的缺陷态的产生。在以MEH-PPV作为发光层的聚合物电致发光器件中,在PEDOT中掺杂二氧化钛纳米管和氧化锌纳米棒后,器件的最大效率分别提高了2倍和2.5倍。     

Some spirobiindane based 1H-pyrazolo [3,4-b] quinoline chromophore as novel chromophore for light-emitting diodes

An influence of phenoxy groups for the luminescent and electroluminescent properties of spiro-compounds with pyrazolo [3,4-b] quinoline structure (fluorophore) chromophore has been studied. All the compounds exhibit strong fluorescence in solution and in solid state as well. The prepared compounds were used as dopant chromophore in PVK polymer matrices for electroluminescent (EL) and light-emitting diode (LED) devices with configuration ITO/PEDOT-PSS/PVK/PQ/Ca/Al. Role of the bathochromic shifts and solvent polarity in absorption and photoluminescent maxima is considered. Relation between the number of pyrazoloquinoline chromophore and presence of phenyl group on the fluorescence spectra is explored. Polarizability of the particular pyrazoloquinoline compounds on the solvatochromic effects is investigated. Possible ways of enhancement of the brightness in the light-emitting properties of the mentioned chromophore are discussed.     

基于MEH-PPV/ZnSe纳米复合器件的电致发光特性的研究

以巯基乙酸作为稳定剂在水相中制备了ZnSe纳米晶,用X射线粉末衍射(XRD)和X射线光电子能谱(XPS)对其进行了表征。用表面活性剂将ZnSe纳米晶从水相中转移到有机相中,使其与聚合物MEH-PPV复合作为发光层,制备了多层电致发光器件Glass/ITO/MEH-PPV∶ZnSe/BCP/Alq₃。对ZnSe纳米晶和MEH-PPV薄膜的光致发光谱及其吸收光谱的比较表明ZnSe纳米晶和MEH-PPV之间存在着能量传递,这是导致纳米复合薄膜的光致发光光谱和电致发光光谱存在差异的原因之一。文章对其在光激发和载流子注入条件下的不同发光机制进行了讨论。通过对器件的光电特性进行研究,发现ZnSe纳米晶发光的比例随着外加电压的增加而增加,而且器件的I-V特性基本上符合二极管的特性。     

Synthesis and characterization of a solution processible deep blue light-emitting molecule composed of fluorene and pyrene units

A solution processible deep blue light-emitting molecule composed of pyrene and dialkylfluorene units, 1,6-bis(9,9′-dioctylfluorene-2-yl)pyrene (BDOFP) was synthesized and characterized. The synthesized compound was soluble in common organic solvents and the solution gave a smooth thin film after spin coating. The compound was characterized by using thermogravimetric analysis (TGA), differential calorimetry (DSC), UV–visible spectroscopy, fluorescence spectroscopy and cyclic voltammetry. The maximum UV–visible absorption and PL emission of BDOFP thin film were more red-shifted than those of BDOFP solution due to strong intermolecular interaction between flat segments. To improve color purity and film stability BDOFP was doped to a well-known charge-transporting polymer, poly(N-vinylcarbazole) (PVK). BDOFP thin film showed it maximum PL at 457 nm but the thin films of BDOFP doped PVK films showed it at 443 nm. Organic light-emitting diodes were fabricated with the simple structure of ITO/PEDOT:PSS/emitter/BmPyPB/LiF/Al configuration. BDOFP or three kinds of BDOFP:PVK blends with different ratios (10:90, 30:70, 50:50 by weight) were used as the emissive layers and [1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene] (BmPyPB) as the electron-transporting layer. All of light-emitting devices showed their electroluminescence in blue region of spectrum, especially EL using BDOFP: PVK (1:9) showed a deep-blue light emission with CIE coordinates of (0.14, 0.07). Maximum brightness, external quantum efficiency and current efficiency of the device were 500 cd/m², 0.7% and 0.44 cd/A, respectively.     

DCM掺杂PVK体系的超快光谱

利用稳态荧光光谱和时间分辨超快光谱研究了DCM掺杂PVK(聚乙烯咔唑)体系的发光特性和能量转移。根据DCM的吸收光谱与PVK的荧光光谱,用Frster理论估算出DCM:PVK掺杂体系能量转移的临界半径及其效率。在DCM:PVK掺杂薄膜中,随着掺杂浓度的升高,DCM的发射强度增强,PVK的发射强度减弱,两者相对强度之比与估算结果一致。还利用时间分辨超快光谱研究了DCM:PVK掺杂薄膜体系的能量转移动力学过程,观察到DCM:PVK掺杂薄膜的荧光寿命随着掺杂浓度的升高逐渐变短。结果表明,在DCM:PVK掺杂薄膜中,存在从PVK到DCM较为有效的Frster能量转移。     

Electroluminescence of CdSe/CdS quantum dots and the transfer of the exciton excitation energy in an organic light-emitting diode

A light emitting diode has been developed on the basis of multilayer nanostructures in which CdSe/CdS semiconductor colloidal quantum dots serve as emitters. Their absorption, photo-, and electroluminescence spectra have been obtained. The strong influence of the size effect and the density of particles in the layer on the spectral and electrophysical characteristics of the diode has been demonstrated. It has been shown that the rates of the transfer of the exciton excitation energy from organic molecules to quantum dots increase strongly even at a small increase in the radius of the core (CdSe) of a particle and depend strongly on the thickness of the shell (CdS) of the particle. The optimal arrangement of the layer of quantum dots with respect to the p-n junction has been estimated from the experimental data. The results demonstrate that the spectral characteristics and rates of the electron processes in light-emitting devices based on quantum dots incorporated into an organic matrix can be efficiently controlled.     

Effect of the <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junction breakdown mechanism on the Er<Superscript>3+</Superscript> ion electroluminescence intensity and excitation efficiency in Si: Er epitaxial layers grown through sublimation molecular beam epitaxy

A series of Si: Er/Si light-emitting diode structures with a smoothly varying p-n junction breakdown mechanism, grown through sublimation molecular-beam epitaxy, is used to investigate the effect of the breakdown mechanism on the electroluminescence of the structures. The maximal intensity and excitation efficiency of room-temperature Er³⁺ ion electroluminescence are shown to be attained in diode structures with a mixed breakdown mechanism.